l60 BULLETIN OF THE BUREAU OF FISHERIES. 



followed by a brief rest period. A young hickory-nut mussel was obser\^ed to travel 

 O.I meter (about 4 inches) in 29 minutes. The rate of travel of sand-shells is much more 

 rapid. 



Because of their small size and delicate shell the early juvenile mussels are doubt- 

 less the prey of numerous enemies. Turbellarian and chsetopod worms are known to 

 devour them. No doubt they are sometimes eaten bj' fish and aquatic animals, such as 

 are accounted enemies of larger mussels, yet there has been found little evidence of 

 serious depredations upon young mussels by such animals. Perhaps the most serious 

 natural mortality among juvenile mussels occurs from falling upon unfavorable bottoms 

 or from the effects of currents, especially in times of flood, which may draw the rela- 

 tively helpless mussels into environments in which they have small chance for survival. 

 It may be expected, too, that the repeated dragging of crowfoot bars over favorable 

 mussel bottoms works damage to juveniles both by injuries directly inflicted and by 

 pulling them from the bottom and exposing them to the action of currents from which 

 they had previously found protection. 



ARTIFICIAL PROPAGATION. 

 PRINCIPLE OF OPERATION. 



As the previous account of the life history of fresh-water mussels has shown, the 

 mussel not only deposits great numbers of eggs but nurtures them in brood pouches 

 within the protection of her shell. There is not, as in fish, a great wastage of eggs and 

 larvae in the very earliest stage of development. There exists, therefore, no necessity 

 for artificial aid to effect fertilization; that is, to bring the male and female reproductive 

 elements together. Nature's own provisions have adequately provided for the bringing 

 of enormous numbers of each generation of offspring to the glochidium stage. It is 

 after this stage is attained that the greatest mortality occurs; the great abundance of 

 glochidia produced by each female is, indeed, evidence that enormous losses are to 

 occur subsequently, and observation indicates that the critical stages are, first, when the 

 glochidia are liberated from the parent to await a host, and, second, when the juvenile 

 mussels are dropped from the fish that serves as host. 



The artificial propagation of mussels as now practiced aims to carry the young 

 mussels through the first great crisis. Its object is to insure to a large number of 

 glochidia the opportunity to effect attachment to a suitable fish. Under present 

 conditions the operations can be conducted extensively and economically only in the 

 field. The procedure in brief is to take fish in the immediate vicinity of the places to 

 be stocked, infect them with glochidia of the desired species of mussels, and liberate 

 them immediately. Artificial propagation, then, as applied to fresh-water mussels, is 

 a very different sort of operation from that employed in the propagation of fish, 

 although it is no less directly adapted to the conditions and needs of the objects to be 

 propagated. 



METHODS. 



In each field the operations are conducted under the immediate direction of a qual- 

 ified person who may be either a permanent or temporary employee of the Bureau work- 

 ing under the Fairport station. The fishing crew is comprised of three or four local 

 fishermen, or laborers, temporarily employed. 



